36. The Relationship Between Behavioural and Physiological Tolerance to Elevated CO2 in Coral Reef Fish

Taryn D. Laubenstein (1)*, Jodie L. Rummer (2), Philip L. Munday (2)

1 College of Marine and Environmental Sciences, James Cook University, Townsville, Qld, 4811, Australia
2 ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Qld, 4811, Australia

Background
Reef fish exhibit both behavioural and physiological sensitivity to elevated CO2. However, individuals within populations demonstrate varying levels of sensitivity to these negative effects. Those individuals that are more tolerant provide hope for future populations to adapt to changing environmental conditions. Yet whether there is an interaction between behavioural and physiological tolerance, which may either constrain or facilitate adaptation, is unknown. We seek to understand the relationship between behavioural and physiological sensitivity to elevated CO2, and how it might be altered by elevated temperature.

Methods
Juvenile Acanthachromis polyacanthus will be reared from birth in one of four temperature x CO2 treatments: control, elevated temperature, elevated CO2, or elevated temperature and CO2. After 40 days, individuals from each treatment will be tested for their behavioural and physiological tolerance to elevated CO2. Behavioural tolerance will be measured as response to chemical alarm cue in a two-choice flume tunnel. Physiological tolerance will be measured as aerobic scope in a custom-built respirometer.

Findings
We predict that a tradeoff will exist between behavioural and physiological tolerance to CO2, where individuals with a high behavioural tolerance will have a low physiological tolerance, and vice versa. Furthermore, we predict that elevated temperature and CO2 together will have an additive or multiplicative effect on physiological tolerance but not behavioural tolerance.

Conclusions
Adaptation to high CO2 could be constrained if behavioural and physiological tolerance to elevated CO2 are negatively correlated at the level of the individual. Selection towards highly tolerant individuals will act orthogonally to the direction of the most genetic variation, and thus adaptation to high CO2 conditions will be limited. However, we predict that elevated temperature and CO2 conditions will lower physiological tolerance across the population. This would increase the importance of behavioural tolerance, and thus push future populations towards an increased behavioural tolerance.